Preheat the oven to 425 degrees. Line a large sheet pan with parchment paper, or spray with non-stick spray.
In a small bowl, whisk together the chili powder, cumin, salt and pepper, coconut oil until combined.
In a large bowl add the chicken, onions, peppers, and pineapple. Drizzle over spice mixture. Toss to coat everything well.
Spread in a single layer onto prepared sheet pan.
Bake in oven for 12 - 15 minutes, until chicken is just about done. Then turn the broiler on a couple of minutes to char the vegetables and brown the chicken a bit more.
If desired, sprinkle with sesame seeds, and then serve.